1. Field of the Invention
The present invention relates to a method and a control circuit for measuring the die temperature of an integrated circuit (IC), such as a microprocessor, that is relatively more accurate than known methods and a control circuit for reducing the clock frequency of the IC during excessive temperature conditions until the temperature returns to normal in order to avoid damage to the IC.
2. Description of the Prior Art
Microprocessors are known to be used in various types of personal computers including notebook and subnotebook computers. The relatively fast clock speeds of the newer microprocessors cause the temperature of the microprocessor to get relatively hot. Due to the relatively compact nature of the notebook and subnotebook personal computers, very little ventilation is available within the computer housing to cool down the microprocessors.
Many integrated circuits (IC), particularly microprocessors, are known to have a die temperature limit of about 100.degree. C. The die temperature relates to the temperature of the die or semiconductor chip that is normally bonded to an outer IC package which includes the terminal pins chip. Die bonding refers to the process in which the semiconductor chip is bonded to a thick film substrate or a base of the outer IC package. Various die bonding methods are known including eutectic alloying, soft soldering and plastic adhesives.
In order to prevent a failure or misoperation of the semiconductor chip or a failure of the bond between the semiconductor chip and its outer IC package, the die temperature of many ICs must be maintained at less than about 100.degree. C. Since the die is within the IC package, there is heretofore been no way to measure the die temperature. As such, an outside surface temperature of the IC package has heretofore been used as an empirical approximation of the die temperature. For example, due to the thermal drop across the outer IC package, an outside surface IC temperature of about 80.degree. C. has been used as an approximation of the 100.degree. C. die temperature limit within the IC package. However, such an estimation is empirical and, thus, relatively inaccurate which could lead to failure of the integrated circuit.
Notwithstanding the inaccuracy of such a measurement, other problems result from measuring the outside surface temperature of the IC package. For example, in order to measure the outside surface temperature of the integrated circuit package, a thermistor or other temperature sensing device is known to be used and disposed to be in contact with the outer IC package. Such devices, in addition to adding to the cost of the personal computer in which they are used, require additional space; normally at a premium within the relatively compact notebook and subnotebook type personal computers.